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Update coherence rules to be more flexible for impl Trait for Type #5515

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Update coherence rules to be more flexible for impl Trait for Type #5515

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95 changes: 49 additions & 46 deletions src/librustc/middle/typeck/coherence.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -104,6 +104,32 @@ pub fn get_base_type(inference_context: @mut InferCtxt,
}
}

pub fn type_is_defined_in_local_crate(original_type: t) -> bool {
/*!
*
* For coherence, when we have `impl Trait for Type`, we need to
* guarantee that `Type` is "local" to the
* crate. For our purposes, this means that it must contain
* some nominal type defined in this crate.
*/

let mut found_nominal = false;
do ty::walk_ty(original_type) |t| {
match get(t).sty {
ty_enum(def_id, _) |
ty_trait(def_id, _, _) |
ty_struct(def_id, _) => {
if def_id.crate == ast::local_crate {
found_nominal = true;
}
}

_ => { }
}
}
return found_nominal;
}

// Returns the def ID of the base type, if there is one.
pub fn get_base_type_def_id(inference_context: @mut InferCtxt,
span: span,
Expand Down Expand Up @@ -161,8 +187,7 @@ pub fn CoherenceChecker(crate_context: @mut CrateCtxt) -> CoherenceChecker {
crate_context: crate_context,
inference_context: new_infer_ctxt(crate_context.tcx),

base_type_def_ids: HashMap(),
privileged_implementations: HashMap()
base_type_def_ids: HashMap()
}
}

Expand All @@ -174,11 +199,6 @@ pub struct CoherenceChecker {
// definition ID.

base_type_def_ids: HashMap<def_id,def_id>,

// A set of implementations in privileged scopes; i.e. those
// implementations that are defined in the same scope as their base types.

privileged_implementations: HashMap<node_id,()>,
}

pub impl CoherenceChecker {
Expand Down Expand Up @@ -615,27 +635,11 @@ pub impl CoherenceChecker {
visit_mod(module_, item.span, item.id, (), visitor);
}
item_impl(_, opt_trait, _, _) => {
let mut ok = false;
match self.base_type_def_ids.find(
&local_def(item.id)) {

None => {
// Nothing to do.
}
Some(base_type_def_id) => {
// Check to see whether the implementation is
// in the same crate as its base type.

if base_type_def_id.crate == local_crate {
// Record that this implementation is OK.
self.privileged_implementations.insert
(item.id, ());
ok = true;
}
}
}

if !ok {
// `for_ty` is `Type` in `impl Trait for Type`
let for_ty =
ty::node_id_to_type(self.crate_context.tcx,
item.id);
if !type_is_defined_in_local_crate(for_ty) {
// This implementation is not in scope of its base
// type. This still might be OK if the trait is
// defined in the same crate.
Expand All @@ -655,25 +659,24 @@ pub impl CoherenceChecker {
implement a trait or \
new type instead");
}
_ => ()
}

for opt_trait.each |trait_ref| {
// This is OK if and only if the trait was
// defined in this crate.

let trait_def_id =
self.trait_ref_to_trait_def_id(
*trait_ref);

if trait_def_id.crate != local_crate {
let session = self.crate_context.tcx.sess;
session.span_err(item.span,
~"cannot provide an \
extension \
implementation for a \
trait not defined in \
this crate");
Some(trait_ref) => {
// This is OK if and only if the trait was
// defined in this crate.

let trait_def_id =
self.trait_ref_to_trait_def_id(
trait_ref);

if trait_def_id.crate != local_crate {
let session = self.crate_context.tcx.sess;
session.span_err(item.span,
~"cannot provide an \
extension \
implementation for a \
trait not defined in \
this crate");
}
}
}
}
Expand Down